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Resistance and Ohm’s Law

Resistance and Ohm’s Law. When electric charges flow they experience opposition or resistance which reduces the amount of energy they have Greater resistance -> greater amount of energy each charge has to give up. Filament – high resistance

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Resistance and Ohm’s Law

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  1. Resistance and Ohm’s Law

  2. When electric charges flow they experience opposition or resistance which reduces the amount of energy they have • Greater resistance -> greater amount of energy each charge has to give up

  3. Filament – high resistance Therefore, lot’s of energy taken from each electron and turned into light Wire – low resistance Therefore, little energy lost – turned mainly into heat

  4. Electric Resistance • The amount of energy (voltage) required to push electrons (current) through a conductor

  5. German Physicist Georg Ohm determined that for a given conductor, the ratio of voltage to current (V/I) is constant • We call this constant resistance (Measured in Ohms - ) = Resistance Constant

  6. Ohm’s Law • Relates voltage, current and resistance • Note: E stands for electric potential (commonly known as voltage)

  7. Electrical Insultator • Prevents the transfer of electric charges • Ex: Air, glass, rubber, paper • Electrical conductor • Low resistance which allows electric charges to flow easily • Ex: copper

  8. Example 1: • A single cell is set-up in a circuit with a switch and a resistor. For the resistor, a voltmeter is set-up and it measures 1.3V and an ammeter is set-up and it measures 3.5A. • Draw the circuit with the correct set-up of a voltmeter and ammeter • Calculate the resistance of the resistor

  9. Example 2: • If a resistor has a resistance of 1000 and the current is 2.0A. What will be the voltage drop across the resistor?

  10. Work • Pg 330 # 1a • Pg 332 # 1, 3-5 • Pg 331 # 5ab,7,8

  11. Circuit Analysis

  12. Types of Circuits • Series • Only one path for current to flow

  13. Types of Circuits • Parallel • More than one path for current to take

  14. Analysis of Circuits • We have four tools we can use to analyze circuits: • Kirchoff’s Current Law (KCL) • Kirchoff’s Voltage Law (KVL) • Ohm’s Law • Equivalent Resistance (Series and Parallel)

  15. Kirchoff’s Current Law (KCL) • At any junction (Point) in the circuit, the current going in equals the current going out • At a point, Iin = Iout • Note: In any series circuit, every point has the same current

  16. Examples

  17. Kirchoff’s Voltage Law (KVL) • In any complete path in a circuit, the sum of voltage rises (sources) is equal to the sum of voltage drops (loads) • For a path, Vrises = Vdrops

  18. Examples

  19. Work • Pg 337 # 1-3 • Pg 343 # 1, 2, 4

  20. Equivalent Resistance • If you have many resistors (or loads) in a circuit, finding the equivalent resistance allows you to replace multiple resistors with a single resistor • This allows easier analysis of circuits

  21. Equivalent Resistance in Series

  22. Equivalent Resistance in Parallel The easiest way to put this formula into a calculator is to use your inverse button (x-1)

  23. Work • Pg 339 # 4-6 • Pg 340 # 7

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